1. Field of the Invention
The present invention concerns the extraction of chemical products, such as wood preservatives, for example, wood posts used in electrical and/or telephone networks, sleepers, and above all any wood article which has undergone a chemical treatment to ensure its preservation and for which discarding is necessary. More particularly, the present invention relates to a process aiming at rendering non toxic a wood which has been treated with pentachlorophenol (PCP) or with any other preservation chemical product (creosote, etc), which process consists in extracting said pentachlorophenol (PCP) or other product (oil, etc) from a wood treated object in order to ultimately give a wood which, after extraction, ceases to constitute a toxic waste according to the environmental regulations presently in force.
2. Description of Prior Art
The destruction of posts treated with pentachlorophenol, by incineration or burying in the ground, is not possible under the present context of environmental concerns, which gives no other alternative to the users than the storage of discarded posts. This alternative involves however a possibility of a risk of contamination which is not negligible on a medium term, and does not constitute a final solution. Since a large number of posts are discarded each year when dismantling or replacing electrical and/or telephone lines or the like, it becomes essential to find a solution to the problem mentioned above, while reducing the risks of contamination to the environment.
The setting up of a treatment center with mechanical, chemical, biological and other means would enable to effect the treatment recommended above; however, such a center would require important investments which would limit the establishment of an important number of plants. Furthermore, one would have to rely on long distance transportation of these articles and even across a border, which would not be necessarily acceptable for the authorities which are responsible for the environment.
A simple and cheap solution, which would involve a technology which has already been tested for other aims, and which could be used locally would by far be desirable by users.
Certain methods of treating wood wastes in order to convert them into useful products, or methods which are used with muds containing preservatives are known, however none of them appear to be capable of solving the problem mentioned above.
Already in 1900, it was suggested to treat used tapestry making devices by treatment with an alkaline solution, followed by steps of washing, bleaching and drying to give a pulp. Reference is particularly made to U.S. Pat. No. 659,715 issued Oct. 16, 1990, inventor Bendix Themans.
U.S. Pat. No. 3,878,994 issued on Apr. 22, 1975, inventor Lion-Hian Tee, describes a method for treating wood waste which would enable to obtain chips which can be used for example in the manufacture of agglomerated panels. This method includes a series of mechanical operations including a reduction of the volume of the wastes by mechanical impact, a coarse separation of the material by flotation, a transformation into chips by crushing, an elimination of the metallic pieces by passing the chips over a screen, a separation of the chips as a function of their size and finally, a washing. This process is limited to the treatment of wood wastes containing no chemical preservatives. Obviously, this process could not be used to extract toxic products from wood.
U.S. Pat. No. 4,666,612 issued on May 19, 1987, inventors Donald G. Hoffman and Thomas L. Hurst, aims at the recovery of preservatives which are present in the aqueous wastes derived from wood treatment plants in order to re-use chemical products. This process is concerned with an intricate method consisting in leading the process liquid wastes to an outside decantation vat and separating the solid and liquid layers which are formed in order to treat them separately in different manners. In this process, the preservatives are concentrated in large part in the solid decantation layer. Again, this is an intricate method which is mainly intended at treating preservatives containing mud.
On the other hand, U.S. Pat. No. 4,797,135 issued Jan. 10, 1989, inventors Josef Kubat and Lars M. Qvist, concerns the pulverization of wood and other types of biomass into powder in order to constitute a fuel for boilers, gas turbines, diesel engines, etc. This method includes pulverizing the original cellulosic material into coarse particles, treating them with an alkaline solution to soften them, exposing them to high temperature, drying them and again pulverizing them to give a powder of adequate granulometry. This process is not at all intended to extract toxic products contained in treated wood.
In U.S. Pat. No. 4,798,651, issued Jan. 17, 1989, inventor Bohuslav Kokta, there is described a method for the preparation of pulp, based on the impregnation of wood chips with an alkaline solution containing an anti-oxidizing agent such as sodium sulfite, followed by a treatment with saturated steam at high temperature and pressure followed by an explosive decompression to give wood particles which are washed and refined to give a pulp.
Finally, U.S. Pat. No. 5,029,299, issued Jul. 2, 1991, inventors Gilbert Guidat and Claudine G. De Queiroz, describes an intricate plant for the production of wood particles including a step of coarse mechanical reduction of the wood wastes, followed by a heat treatment in a rotary oven, a supplementary step of mechanical reduction of the cellulosic material, a chemical treatment of the particles with salts and finally bagging of the finished product.
To this day there is no description of an efficient method, which is easy to use and is of simple design enabling to extract chemical preservatives from wood products.